The present invention relates to a direct positive photographic light-sensitive material. In particular, the present invention relates to a direct positive photographic light-sensitive material which has a high granularity, a soft tone, and a high picture quality.
It is known that a reversed image can be obtained by a process which comprises developing internal latent image-type silver halide grains each composed of (a) a silver halide core which has been doped with a metal ion and/or chemically sensitized, and (b) a silver halide shell covering at least a sensitive site of the core, the shell surface being, if necessary, chemically sensitized and, (b) a silver halide shell covering at least a sensitive site of the core, the shell surface being, if necessary, chemically sensitized (these grains are hereinafter referred to as "core/shell-type grain"), in the presence of a fogging agent, or according to a direct reversal process wherein the development is conducted under overall light exposure. Such a process is described in U.S. Pat. Nos. 3,317,322 and 3,761,276.
Such a core/shell type silver halide emulsion has a drawback in that the gradation is hard and a sensitive material capable of realizing a soft tone and a high picture quality cannot be obtained therefrom, because the emulsion is of a monodisperse system. It is known that such a defect can be overcome to some extent by forming a layer of a mixture of emulsions having the same color sensitivity but different sensitivities, or by arranging those emulsions in two layers as disclosed in Japanese Patent Public Disclosure No. 56142531.
The use of a silver halide photographic light-sensitive material having two layers comprising the core/shell-type silver halide grains as described above provides an excellent reversed photographic property with respect to a gradation. However, there is a drawback in that other photographic properties such as a granularity and black spot inhibition are poor. Supposedly, when two kinds of emulsion layers are formed so as to obtain a soft tone, the development of the emulsion layer of higher sensitivity induces the development of the emulsion layer of lower sensitivity. This will seriously damage the granularity.
Further, when several kinds of emulsions are prepared by using the same apparatus, a direct positive emulsion having a higher sensitivity happens to be contaminated by a negative emulsion and, therefore, an emulsion having a lower sensitivity is influenced by the contamination of the negative emulsion even though the operation is carefully conducted so as to prevent the contamination with the negative emulsion. As a result, spots, namely, black spots are formed and seriously damage the picture quality.
The term "black spot" as used herein indicates those formed on a portion where the density must be uniform. They are also called "black pepper". In a color photo-sensitive material, the spots have colors such as yellow, magenta and cyan depending on the emulsion layer formed.
These defects can be overcome by modifying the developability of the emulsion of higher sensitivity, or by preparing this emulsion carefully so as to avoid the contamination thereof with the negative emulsion. However, other photographic properties are seriously modified in the former method, while the production cost is increased in the latter method.